Method of fitting a prosthetic device for providing corrections of auditory deficiencies in aurally handicapped persons

ABSTRACT

The method of fitting a prosthetic device for providing compensatory amplification for aurally handicapped persons. The method includes the steps of determining absolute threshold information and tone discomfort information and coupling the subject to a master hearing aid which includes a filter network selected to be in the general range of the acuity deficiency as determined by the above information. Then, forced-choice pairedcomparison techniques, using continuous discourse, gives the required information for selecting the appropriate filter, filter gain and flat gain parameters to be used as a single filter network in a prosthetic device.

United States Patent Stearns et al.

[ Nov. 12, 1974 METHOD OF FITTING A PROSTHETIC 2,768,236 l0/l956 Allison179/1 N DEVICE OR PROVIDING CORRECTIONS 3,404,235 10/1968 Goldberg 179/1N 01111 222122; 211221 2:11;: 1221:: AURALLY HANDICAPPED PERSONS [75]Inventors: William P. Stearns, Scottsdale; primary Emminer R-a|phBiukcslec g f Elpem, Phoemx, both of Attorney, Agent. or FirmLy0n andLyon [73] Assignee: John L. Holmes, Scottsdale, Ariz. 5 ABSTRACT [22]Filed: 1973 The method of fitting a prosthetic device for providing 21App] 350 377 compensatory amplification for aurally handicapped persons.The method includes the steps of determining absolute thresholdinformation and tone discomfort [52] US. Cl 179/1 N, 181/.5 G, 179/107 Finformation and coupling the subject to a master hear- 128/2 Z ing aidwhich includes a filter network selected to be [51] Int. Cl H04! 25/00in the genfiral range of the acuity deficiency as damp [58] F'eld ofSearch 107 107 FD; mined by the above information. Then, forced-choice181/5 G; 128/2 Z paired-comparison techniques, using continuousdiscourse, gives the required information for selecting [56] Referencescued the appropriate filter, filter gain and flat gain parame- UNITEDSTATES PATENTS ters to be used as a single filter network in aprosthetic 2,112,569 3/1938 Lybarger 179/1 N device.

2,394,569 2/1946 Strom l79/l N 2,625.233 1/1953 Curry??? 179/1 N 14Clam, 9 Drawlng Flgul'es PATENI w 1 21 974 3.848.091 SNEEIHF 4 QSNNQQMETHOD OF FITTING A PROSTHETIC DEVICE FOR PROVIDING CORRECTIONS OFAUDITORY DEFICIENCIES IN AURALLY HANDICAPPED PERSONS CROSS-REFERENCE TORELATED APPLICATIONS The present application is directed to inventiveconcepts which are related to those described in copending applicationSer. No. 133,229, filed Apr. 12, 1971 by William P. Stearns andentitled, Method and Apparatus for Providing Electronic SoundClarification for Aurally Handicapped Persons". The present applicationalso is related to co-pending applications, Ser. No. 229,322 filed Feb.25, 1972 in the names of William P. Stearns and John K. Lauchnerentitled, Apparatus and Prosthetic Device for Providing ElectronicCorrection of Auditory Deficiencies for Aurally Handicapped Persons, andSer. No. 229,398 filed Feb. 25, 1972 in the names of William P. Stearnsand Barry S. Elpern entitled Method for Providing Electronic Restorationof Speech Discrimination in Aurally Handicapped Persons. The presentapplication also is related to the co-pending application Ser. No.350,415 filed Apr. 12, 1973. concurrently filed herewith in the names ofWilliam P. Stearns, Vernon O. Blackledge and John S. Rohrer, entitledProsthetic Device for Providing Corrections of Auditory Deficiencies inAurally Handicapped Persons which describes and claims apparatusdisclosed herein. All of the above cited applications are assigned tothe assignee of the present application and the disclosures thereof areincorporated herein by reference.

BACKGROUND OF THE'INVENTION This invention relates to the soundamplification arts, and to their application in the amelioration ofauditory deficiencies resulting from damage to the sensorineuralstructures of the human ear. It relates particularly to methods forcorrecting deficiencies in a persons ability to perceive and tocomprehend spoken language.

Sensori-neural hearing loss is generally considered to be the mostprevalent type of auditory handicap found in the United States as wellas in other civilized cultures. It constitutes a significant barrier toadequate communication in 5 to percent of the total United Statespopulation, and in more than 50 percent of the opulation over 60 yearsof age. Furthermore, these proportions are expected to increase inconjunction with ongoing increases in ambient noise levels and lifeexpectancy in our society.

Sensori-neural impairment may result from any one or more of a number ofcauses, including, but not limited to genetic and congenital factors,viral diseases,

specific toxic agents, circulatory disturbances, specific physicaltraumaand excessive exposure to noise. Irrespective of the primarycause, however, sensory cells within the organ of hearing or theirassociated neural units suffer some degree of damage and are renderedpartially or totally incapable of fulfilling their respective roles inthe processing of auditory information. This form of damage cannot berepaired by means of currently known medical or surgical techniques, andthe probability of discovery of effective techniques within theforeseeable future appears rather remote. Thus, in virtually all casesof sensori-neural hearing loss, amplification of incoming soundsrepresents the only possible means for restoring adequate hearingability.

Hearing loss resulting from sensori-neural damage is usually irregularwith respect to frequency, being selectively greater for particularportions of the audible frequency range. The ability to hear sounds inthe range above 1,000 Hz is often affected more than the hearing ofsounds below 1,000 Hz, although this is by no means a universalobservation. The ultimate consequence of irregular hearing acuity forvarious portions of the audio frequency spectrum is distortion in theperception of complex sounds, i.e., sounds composed of a number ofdifferent frequencies.

A certain amount of distortion in complex sounds may be tolerable, butcurrent information does not permit precise specification of the maximumamount of each type of distortion which may exist without interferingmaterially with accurate sound recognition. Many gross sounds, forexample, do not demand a great deal of analytic power in the auditorysystem, so even a rather severely impaired system may functionadequately in the interpretation of such sounds.

In audiologic parlance, the term discrimination denotes the capacity ofthe ear to analyze incoming acoustic patterns and interpret themappropriately. Analytic power may fail at any of several stages in theauditory process, commonly in the organ of hearing or first orderneurons due to damage to these structures. Since the ear may be requiredto perform many degrees of discrimination, varying from extremely coarseto extremely fine, its analytic power may be measured through the use oftests which demand auditory discriminations of progressive difficultyuntil failure occurs.

Among the most difficult discriminations required of the human ear arethose necessary for accurate interpretation of speech, particularlyspeech in the presence of noise. Because of the fundamental importanceof spoken communication, it is obvious that chronic inability tounderstand what people say could profoundly influence an individualssocial, economic and cultural well-being. Tests of speech discriminationare commonly employed, therefore, to derive a realistic estimate of apersons everyday functional adequacy in hearing.

Each of the phonic units of a spoken word is a complex sound, composedof several frequencies clustered in a more-or-less definable range. Whenthe acuity of the ear has been selectively impaired in a specificfrequency range, speech sounds or their components falling in that rangemay be heard at reduced intensity or not at all. Impairment in severalfrequency ranges compounds the difficulty and is probably responsible inlarge measure for the primary complaint of the individual withsensori-neural hearing loss, that he can hear a speakers voice butcannot understand what is said. The mechanism for inhibiting suchunderstanding may be the non-linear responses that result inintermodulation products and harmonics which could cause interferencewith the desired spectral components of speech.

On the basis of the foregoing information, it would seem quitereasonable to deal with scnsori-neural hearing loss by selectivespectrum amplification; that is, providing amplification only in thosefrequency ranges or bands in which acuity is deficient, and only in theamount of the deficiency. Thus, the ultimate value of selective spectrumamplification rests on the application of appropriate methods formeasuring the degree of auditory deficiency as a function of variousfrequency bands, and also on the construction of a wearable device whichis fully capable of producing amplification to compensate for themeasured deficiencies. Because of existing inadequacies in bothrespects, the principle of selective amplification has fallen intodisrepute, for the hearing aid industry has adopted the pure tone(single frequency) threshold audiogram as the criterion measurement, andhas produced hearing aids with inadequate capabilities for providingproper acoustic output at each portion of the audio band.

The threshold audiogram curve represents an individuals measuredabsolute auditory threshold for a series of pure frequency tones,usually in the range of 250 Hz to 8000 Hz sampled at octave intervals onthe assumption that intra-octave tone thresholds follow the generalaudiogram contour. However, it is demonstrable that fairly markeddepartures from this overall pattern may exist at intermediatefrequencies, i.e., frequencies between pure tones one octave apart.

The rationale for utilizing threshold measurements is shrouded inhistory, but it is exceedingly interesting to note that the analogousprocedure of measuring visual thresholds for monochromatic (singlecolor) lights is never performed to measure the visual acuity of the eyeor to prescribe eyeglasses. In fact, careful consideration of the typesof measurements which are genuinely helpful in guiding the design ofparticular hearing aid features suggests that the pure tone thresholdcurve is virtually useless for several reasons:

A. Under everyday circumstances, individuals react only tosupra-threshold sounds, as these are the sounds of primary significance.For practical purposes, threshold sounds remain unnoticed.

B. The contour of an individuals threshold curve is observably differentfrom the contour of his suprathreshold equal loudness curves orcomfortable listening level curves.

C. An individuals recognition of complex phonic units or theircombination into spoken words is essentially unrelated to his acuity forindividual pure tones.

Control of acoustic output in current hearing aids is ordinarilyachieved through manipulation of frequency response, which refers to theacoustic output of a sound transmission system at each of thefrequencies within its pass band when the input level is maintainedconstant for all frequencies. A graphic representation of a systemsfrequency response is referred to as a response characteristic, curve orcontour. Manufacturers com- Imonly claim that they are able to buildhearing aids to One additional comment is relevant as a preface to theinnovative concepts to which the present invention is particularlyaddressed. It is generally recognized that the ear with sensori-neuralhearing loss is excessively susceptible to overloading, which is to saythat, although it may-be relatively insensitive to sounds of low ormoderate intensity, it is hypersensitive to sounds of higher intensity(i.e., non-linear response characteristics). This condition restrictsthe useful operating range of the ear, referred to as the dynamic range;that is, the decibel difference between the lowest intensity at which asound is reliably detected (absolute threshold) and the upper limit ofcomfortable loudness for that sound (discomfort threshold).

Whereas the dynamic range of the normal ear is of the order of dB, therange of a sensori-neurally impaired ear may be as little as 10 or 15dB, generally over a limited frequency spectrum range. Thus, for animpaired ear to function with any degree of adequacy, the full intensityrange of the outside acoustic world must be restricted in some way tofit through an abnormally small sound window and such restriction mustcause minimal intermodulation products, harmonics, and so forth whichwould result in distortion. Without such restriction, the ear is readilyoverloaded, leading to psychologic or physical annoyance and distortionof incoming acoustic patterns.

The consequences of overloading have been appreciated for many years,and output compression devices are widely used in todays hearing aids.Without exception, however, these devices operate on a broad frequencyband, so that when any frequency component of a signal reaches apredetermined critical level, the entire pass band of the hearing aid iscompressed. Consequently, the components which are not at a criticalintensity are needlessly attenuated.

Our evaluation of relevant factors has led to the evolution of severalinnovative concepts concerned with improved methods and apparatus formeasuring and describing auditory deficiency for purposes of prescribingcompensatory amplification, and with improved methods and apparatus forproviding such compensatory amplification in practical and wearableform.

SUMMARY OF THE INVENTION While the present application and thepreviouslymentioned, concurrently-filed application include similardisclosures, for the sake of completeness, the claims of the presentapplication are particularly directed to methods of the nature disclosedherein and equivalents thereof for enabling the objectives set forthherein to be accomplished. Accordingly, it is an objective of thepresent application to provide an electronic correction system with thefollowing capabilities:

a. Division of the audible frequency spectrum into two or more adjacentfrequency bands through the use of a filter network. The width andlocation of these bands are adjustable. They can be set so as to closelyfit the patients required response curve. This required curve may bedetermined by the method as defined in the previously mentioned U.S.Pat. application No. 229,309 entitled Method for Providing ElectronicRestoration of Speech Discrimination in Aurally Handicapped Persons inthe names of Stearns and Elpern filed Feb. 25 1972, which application isassigned to the assignee of the present application and the disclosureof which is incorporated herein by reference;

b. specific and individual intensity or volume control associated witheach of the frequency bands defined in (a) above;

c. specific and individually adjustable output compression associatedwith each of the bands defined in (a) above;

d. electro-meehanieal transduction of electronically processed signalsinto acoustical signals, such transduction occurring within the externalauditory canal of the test subject; and

e. pre-amplification and mixing of input signals for broadband intensitycontrol.

Another object of this invention is to provide a method of fitting aprosthetic device for providing corrections of auditory deficiencies inaurally handicapped persons to be accomplished by electronic techniques.

BRIEF DESCRIPTION OF THE DRAWINGS The invention both as to itsorganization and principle of operation together with further objectsand advantages thereof may better be understood by referring to thefollowing detailed description of an embodiment of the invention whentaken in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram illustrating an exemplary embodiment of thebasic concepts utilized in the present invention to provide compensatoryamplification in accordance with this invention.

FIG. 2 is a circuit diagram of an exemplary embodiment of the basicconcepts utilized in the present invention to provide compensatoryamplification in accordance with this invention.

FIG. 3 is a circuit diagram of a highpass filter network utilized inaccordance with this invention.

FIG. 4 is a circuit diagram of a bandpass filter network utilized inaccordance with this invention.

FIG. 5 is a circuit diagram for an alternate embodiment of a summingamplifier in accordance with this invention.

FIG. 6 is a diagram of highpass response curves in accordance with thisinvention.

FIG. 7 is a diagram of bandpass response curves in accordance with thisinvention.

FIG. 8 is a system block diagram of apparatus for the testing methodutilized in accordance with this invention.

FIG. 9 is a system block diagram of apparatus, including details of themaster hearing aid unit in the system of FIG. 8 of the testing method inaccordance with this invention.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to FIG. 1, a basichearing aid is illustrated which can be employed to duplicate a subjectsrequired response curve in a manner described subsequently. Theresulting hearing aid will be wearable and may be as small as practicaland readily adapted to be manufactured in a miniaturized wearable form.The basic components of such a hearing aid include a transducer, such asa miniature ceramic microphone 11, including a built-in, low noise,field effect transistor amplifier. A unit similar to the Knowles BL-l67lmay readily be employed in the practice of this invention as a suitabletransducer stage. Such a unit has a frequency response from less than100 Hz to greater than 8,000 Hz, as measured by standard hearing aidmicrophone measurement techniques. Microphone 1 l is such a unit andreceives power for its built-in field effect transistor (PET) amplifierfrom a 1.3 volt DC source The output of the microphone 11 is connectedto an input of a broadband automatic gain control (AGC) 12.

The broadband AGC output is connected to an input of a preamplifier 13.Preamplifier 13, as is well known in the art, may incorporate aninternally compensated circuit, such as an integrated operationalamplifier similar to Fairchild 776. The preamp 13 may precede thebroadband AGC 12 without altering the effect of the units. The preamp 13may also be an integral part of the broadband AGC 12. The output of thepreamp 13 is to an input of a flat gain control 14 and an input of afilter AGC 15.

The output of the filter AGC 15 is connected to an input of an activefilter network 16. The filter network 16 comprises a filter arrangementsuch as a highpass filter (in FIG. 3) or a bandpass filter (in FIG. 4)and may include a plurality of filters or filter types to provideflexibility to achieve individualized auditory compensation. Thebroadband AGC 12 provides compression over the whole audio spectrum (toprevent loud inputs from producing discomfort and/or amplifiersaturation), and the filter AGC 15 provides for additional compressioncontrol over a predetermined portion of the audio spectrum which dependsupon the selected filter network 16. Thus the dual AGC system 12 and 15provides two functions: 1) it prevents discomfort and- '/or amplifiersaturation and 2) it provides decreasing high-frequency emphasis forlouder sounds. Previously mentioned applications Ser. No. 229,322 andSer. No. 229,398 described the importance of fitting the filter curve toa patients conversation-level loudness curve and not to histhreshold-level curve. Thus, filter AGC 15 allows the fitting to boththese curves simultaneously. The filter AGC 15 and the filter 16 can beinterchanged without affecting performance.

The output of the flat gain control 14 is connected to a first input ofa summation amplifier 17. The output of the filter 16 is connected to asecond input of the summation amplifier 17. The signals at the first andsecond inputs of the summation amplifier 17 are linearly summed in thesummation amplifier 17. The output of the summation amplifier 17 isconnected to an input of a volume control 18, which attenuates theoutput signals from the summation amplifier 17 before feeding thesiganls to a miniature magnetic receiver 19. The output of the summationamplifier 17 is also connected to an input of an automatic gain controldetector 60, which in turn is connected at its output to a second inputof the broad band automatic gain control 12 and a second input of thefilter automatic gain control 15.

In operation, a DC supply, such as rechargeable or long-life batteries,provides a power source which allows the acoustical input signals to befed from the microphone 11 to the broadband AGC 12.

The preamplifier l3 and the associated broadband automatic gain control12 amplify and compress the signals from the microphone 11 and drive thefilter AGC 15 and the flat gain control 14. The filter automatic gaincontrol 15 compresses the filtered frequencies by an amount determinedby the automatic gain control detector 60. The filter network 16 has anactive bandpass or highpass filter configuration dependent on thepatients hearingproblem. The two signals from the flat gain control 14and the filter network 16 are each fed to the summation amplifier 17 tobe summed and trol signals to the broadband automatic gain control 12and the filter automatic gain control to control the overall compressionand the filter compression. The wearable hearing aid described hereinpermits a substantial size reduction. Ease of repair, ruggedness, andwaterproof scaling of the electronic circuits can be readilyaccomplished. Attractive and compact packaging for post-auricular(behind the ear) fittings can be provided in that the total circuitherein discussed is readily adaptable to commonly known integratedcircuit techniques.

Referring now to a more specific discussion of the electronics circuitryutilized in the practice of this invention, the circuit of FIG. 2illustrates the miniature ceramic microphone 11 which included abuilt-in, low noise, field effect transistor amplifier and is utilizedas an input transducer. The input signals received at the microphone 11are fed through the broadband automatic gain control network 12 to aninput of an operational amplifier, which serves as the preamplifier 13.The output of the preamplifier 13 is passed through the filter automaticgain control network 15 to the input of a filter driver 16A. The outputof the preamplifier l3 also is connected to the flat gain control 14.Filter network 16 receives its input from the filter driver 16A and inturn is connected to an input of an operational amplifier employed asthe summation amplifier 17. A second input of the summation amplifier 17is connected to the flat gain control 14. The output of the summationamplifier 17 is connected to the volume control 18, which in turn isconnected to the receiver 19. The output of the summation amplifier 17is also connected to the input of an automatic gain controlpotentiometer 60A, which is connected to the input of a peak detectorcircuit 60B. The two of which serve as the automatic gain controldetector 60.

The operational amplifiers of FIG. 2 may be any state-of-the-art unitssuch as Fairchild 776, which uses a 2.7V supply; or units that operatefrom a single 1.3V supply, or any number of similar units.

The circuit of FIG. 2 preferably employs a miniature magnetic receiver19 at the output of the summation amplifier 17. Various miniaturemagnetic receivers can be connected to a driver circuit of a hearingaid, de-

pending on the patients requirements, i.e., for persons requiring morevolume, larger diaphragm receivers can be used. Smaller receiverscapable of being placed entirely within the ear channel can also bedriven by the same driver stages.

In FIG. 2, the negative input of the amplifier 17 is used to sum bothsignals from the flat gain control 14 and the filter network 15. Thisprovides same-poiarity summing. If an operational amplifier withdifferential inputs is used, it is also possible to sum the input fromthe filter network 16 into the negative (inverting) input and the inputfrom the flat gain control 14 into the positive (non-inverting) input toprovide opposite polarity summing as is illustrated in FIG. 5. This maybe necessary dependent upon the filter characteristics.

In FIG. 5, the summation amplifier 17 has the input from the flat gaincontrol connected to its positive (non-inverting) input and the input(s)from the filter(s) connected to its negative (inverting) input. Thisallows a smoother frequency response when used with some types offilters.

FIG. 3 illustrates a 7-pole highpass filter, including three operationalamplifiers 25, 26 and 27 in an active filter configuration. A suitablefilter has its break frequency capable of being placed anywhere from 200Hz to l0,000 Hz. Adjusting the proper resistors (28, 29 and 30)determines the precise break frequency, and adjusting the properresistors (31, 32, 33) determines the Q of each 2-pole section. Theoutput of the highpass filter is linearly summed with the output of theflat gain control in the summation amplifier as previously described.

Referring now to FIG. 4, there is illustrated a 6-pole bandpass filterincluding three operational amplifiers 34, 3S and 36 in an active filterconfiguration. As in FIG. 3, any filter can be designated such that itscenter frequency can be placed between 200 Hz to 10,000 Hz. Adjustingthe proper resistors (37, 38 and 39) determines the precise centerfrequency, and adjusting the proper resistors (40, 41 and 42) determinesthe Q of each 2-pole section. The output of the bandpass filter islinearly summed with the output of the fiat gain control in thesummation amplifier as previously described. As in FIG. 3, the filtersutilized may have a gain of from 0 dB to 40 dB or more. A typical gainin an embodiment of this invention would be 30 dB.

FIG. 6 and FIG. 7 illustrate highpass and bandpass response curvesrespectively. Further, FIGS. 6 and 7 illustrate how the fiat gain can beadjusted in relationship to the filter gain. Once the filter has beentuned, a definite frequency response is obtained. The flat gain controlprovides a convenient method for raising or lowering the flat gain areaof the curves in FIGS. 6 and 7 in relationship to the filter gain area.FIGS. 6 and 7 both illustrate two different flat gain control settings.The flat gain control settings being at approximately 30 and 40 dB.

The filter network 16 of FIG. 2 may be comprised of 2-pole, 3-pole,4-pole, 5-pole, 6-pole or greater, highpass or bandpass filterconfigurations or combinations thereof to provide the desired response.More poles are generally required to provide steeper slopes.

Referring now to the system block diagram of FIG. 8, in the operatemode, a pure tone source 40 (such as a Wavetek is connected through aswitch 51 to an input of a pulser 41, which in turn is connected at itsoutput to an input of an amplitude modulator 42. The pulser 41 gates thetone from the source 40 at a rate from 2 to 10 Hz and a 50 percent dutycycle. The low frequency and the high frequency are so chosen that thepatient wontt think the tone is continuous. The purpose of the pulser isto prevent fatiguing the patient and to allow easier recognition. Hegets tired quicker if the tone is not pulsed. Some patients find certainpulse rates more desirable than other rates. The amplitude modulator 42varies in magnitude of the pure tone from the pulser 41 exponentiallywith time (or with DC control voltage) at a rate of approximately 2 dBper second, increasing if an associated hand held switch 43 is notpressed. The amplitude modulator 42 possesses a dynamic range of 120 dBin order to permit traversal of virtually the entire range of humanhearing (typically I34 to dB SPL at l KH The amplitude modulator 42 hastwo outputs. The amplitude-modulated, pulsed pure tone output is fed toa first input of a summation amplifier 44, the output of which isconnected to a patients receiver 45. A DC voltage which corresponds tothe logarithm of the amplitude of the pure tone is fed to the Y input ofan XY recorder 46 in the operate mode through a switch 61. A suitable XYrecorder 46 is the Esterline Angus XY 8511. A second output from thepure tone source 40, which corresponds to the logarithm of the frequencyof the pure tone, is connected to the X input of the XY recorder 46. Thepure tone source 40 is designed to automatically sweep exponentiallyfrom 100 Hz to 10,000 Hz at a sweep speed of approximately one octaveper minute.

In a calibration mode the output from the pure tone source 40 isconnected through the switch 51 to an input of an attenuator 47 whichprovides means for attenuating the tone to be fed to an input of theMaster Hearing Aid (MI-IA) 49 through 'a switch 52 (with a sound fieldand a test tone mode). The output of the MHA 49 in the calibrate andtest tone mode is connected through a switch 62 (with a sound field anda test tone" mode) to an input of the log converter 50. The logconverter 50 provides a DC voltage through switch 61 to the Y input ofthe XY recorder 46, corresponding to the logarithm of the amplitude ofthe pure tone output of the Master Hearing Aid 49. With the puretone'source 40 set to sweep, the response of the MHA 49 is plotted onthe XY recorder 46.

FIG. 9 includes details of the Master Hearing Aid 49. A ceramicmicrophone 48, which includes a built-in field effect transistor, isconnected to an input of a microphone preamplifier 53 in the MasterHearing Aid 49 when the switch 52 is in the sound field mode. Thereamplifier 53 provides amplification prior to signals reaching a filternetwork. The signal from the output of the preamplifier 53 takes tworoutes, one through the filter network illustrated as filters 54, 55, 56and one route through a fiat gain attenuator 59.

The outputs of the filters 54, 55 and 56 (three filters being chosen forconvenience of illustration) are connected to inputs of a filterselector and/or attenuators unit 57. The unit 57, depending on theMaster Hearing Aid 49, might select a single filter, or on anothermaster hearing aid unit, might attenuate each of a plurality of filtersseparately.

The output (or outputs) of unit 57 is connected to a first input of asummation amplifier 58, and an output of the flat gain attenuator 59 isconnected to a second input of the summation amplifier 58. The signalsfrom the two previously mentioned routes arrive at the summationamplifier 58 and, at the output thereof are fed through switch 62 in itssound field mode and summation amplifier 44 to an associated receiversuch as the patients receiver 45, all as illustrated in FIG. 8.

In operation and referring to FIG. 8 in the operate mode, to obtain anabsolute auditory thresholdcurve, the test stimulus from the pure tonesource 40 is a pure tone of gradually increasing frequency fromapproximately 200 Hz to 10,000 Hz pulsed at a rate from 2 to ID pulsesper second by the pulser 41. The subject controls the intensity of thetone by means of the hand held switch 43-or the like. The subject causesthe tone intensity to decrease to a just-inaudible level, immediatelyafter which he causes the tone to increase to a justaudible level,repeating this procedure continuously as the tone frequency increasesgradually. The results are readily recorded in ink on semi-log paper andprovide data regarding the absolute threshold for pure tone as afunction of frequency in the XY recorder 46.

To achieve information as to the auditory discomfort level for puretones, the same test stimulus as utilized in obtaining information as toabsolute auditory threshold for pure tones is utilized. The subjectagain (referring to FIG. 8 in the operate mode) uses the hand heldswitch 43 to control the intensity of the tone. The subject causes thetone intensity to increase to a level of distinct discomfort immediatelyafter which he causes the tone intensity to decrease to a level which istolerable, repeating this procedure continuously as the tone frequencyincreasesgradually. The results are recorded in ink on semi-log paper onthe XY recorder 46 and provide data regarding intensity as a function offrequency which produces auditory discomfort.

From the observed results of the absolute threshold and the auditorydiscomfort curves, as obtained in the above manner, a hearing examinerwill select a general filter network of a type (e.g., bandpass orhighpass) and frequency range so corresponding to the broad range ofacuity deficiency. Such filter (e.g., 54, 55, or 56 in FIG. 9) or filtercombination, is initially selected to generally provide compensatoryamplification in steps in the general frequency band which requiresamplification. To determine more precisely the proper range and typeselection to be made, the two curves mentioned previously may be used todetermine the patient's required response curve in a manner disclosed inthe previously mentioned U.S. Pat. application No. 229,309.

Referring now to FIG. 9 in the sound field mode, the receiver is coupledto the subjects ear by means of a custom fitted earmold or the like. Thestimulus fed to the microphone 48 is recorded continuous discourse,preferably a short paragraph which is reiterated. The subject isrequired to make a forced-choice judgement, as the examiner presents themaster hearing aid parameters in pairs. The individual filters (e.g.,54, 55 and 56) may be of any practical number to divide the selectedbroad frequency range into narrow ranges. For

. example, the subject listens to a brief period of continuous discoursewith the master hearing aid set at a highpass filter number 54, and thento a similarly brief period of continuous discourse with the masterhearing aid set at a highpass filter number 55. The subject is thenrequired to choose which condition was best.

By using similar forced-choice paired comparison the best condition isdetermined for each parameters. The Master Hearing Aid 49 is then soset, and, the calibration mode of FIG. 8 is used to record on recorder46 the final prescription or curves from which the examiner determinesthe filter, filter gain and flat gain combination which will provide thebest qualitative performance and which will be implemented in a systemsuch as FIG. 1 as a single filter network.

The subject is then coupled with an appropriate hearing aid, such as theMaster Hearing Aid 49, which hearing aid has its parameters adjusted asdescribed above. A recorded formalized word test, such as C.l.D.Auditory Test W-22 is then administered at a conversational loudnesslevel, i.e., 65 dB S.P.L. and the subjects score on such test is noted.If the score obtained on the word test is not satisfactory, i.e., lessthan percent, the above tests as to the forced-choice paired comparisonmay be readily repeated.

Further refinements may be accomplished through analysis of informationobtained on an accompanying questionaire, which will provide dataregarding the subjects qualitative evaluation of the hearing aid in reallife listening conditions.

A method is provided which determines absolute threshold and discomfortinformation over a predetermined audio range. The subject is thencoupled to a master hearing aid which includes a filter network selectedto be in the broad range of the acuity deficiency as determined by theabove information. After a forced-choice paired comparison techniquebetween individual filters in the selected filter network, theappropriate parameters are determined to achieve with a single filternetwork, compensatory amplification in a prosthetic device in apractical wearable form.

lt has been pointed out earlier that attempts to compensate for asubjects hearing loss by adjusting the frequency response of an acoustictransmission system so that such response mirrors the subjects absoluteauditory threshold are largely futile, simply because humans do notrespond to threshold stimuli in real-life listening situations. Onlysupra-threshold stimuli are of significance to the subject, and it iswell known that the frequency response of the ear to supra-thresholdstimuli is markedly different from its response to threshold stimuli.Ideally, then, an acoustic transmission system designed to compensatefor hearing loss should provide a frequency response which varies sothat it is appropriate for low intensity stimuli when low intensitystimuli are present, and for high intensity stimuli when high intensitystimuli are present.

While embodiments and applications of this invention have been shown anddescribed, it will be apparent to those skilled in the art that manymore modifications are possible without departing from the inventiveconcepts herein described. The invention thereof is not to be restrictedexcept as necessary by the prior art and by the spirit of the appendedclaims. What is'claimed as new and desired to be secured by LettersPatent of the United States is:

1. A method of fitting a prosthetic device having a single filter and afiat gain control by-passing said filter for providing corrections ofauditory deficiencies in an aurally handicapped subject comprising thesteps of:

. 1. determining absolute threshold information over a predeterminedaudio range for a pure tone as a function of frequency, I

2. determining information over a predetermined audio range for tonediscomfort level of a pure tone as a function of frequency;

3. providing the subject with an output from a master prosthetic deviceincluding a general filter network over a general range of acuitydeficiency of the subject as determined by the results of step 1 andstep 2. said general filter network including a plurality of individualfilter networks;

4. providing the subject with a choice as to the better perception ofcontinuous discourse between discourse at the output of the masterdevice when the master device is set at different individual filternetworks;

5. determining the best individual filter network to provide correctionsof auditory deficiencies in the aurally handicapped subject in responseto the results of step 4, and

6. choosing the prosthetic device having a single filter with the saidcharacteristics of said individual filter network.

2. The method as in claim 1 wherein step 1 further comprises the stepsof:

a. generating a signal of gradually increasing frequency from 200 Hz to10,000 Hz of a pure tone;

b. pulsating the signal at at a comfortable number of pulses per secondthereby forming a test stimulus; and

c. controlling the intensity of the tone of the test stimulus to achieveabsolute threshold information.

3. The method as in claim'2 wherein step (0) further includes the stepsof:

aa. causing the tone intensity to decrease to an approximate inaudiblelevel;

bb. causing the tone intensity to increase to an approximate barelyaudible level; and

cc. repeating steps (aa) and (bb) continuously as the tone frequencygradually increases.

4. The method as in claim 1 wherein step 2 further includes the stepsof:

a. generating a signal of gradually increasing frequency from 200 Hz to10,000 Hz of a pure tone;

b. pulsating the signal at 2 to 10 pulses per second thereby forming atest stimulus;

c. controlling the intensity of the tone of the test stimulus to achieveauditory discomfort information.

5. The method as in claim 4 wherein step (c) further includes the stepsof:

aa. causing the tone intensity to increase to a level of distinctdiscomfort;

bb. causing the tone intensity to decrease to a tolerable level;

cc. repeating steps (aa) and (bb) continuously as the tone frequencygradually increases.

6. A method of fitting a prosthetic device having a single fitter and aflat gain control by-passing said filter for providing corrections ofauditory deficiencies in an aurally handicapped subject comprising thesteps of:

l. generating a signal of gradually increasing frequency from 200 Hz to10,000 Hz of a pure tone;

2. pulsating the signal at two pulses per second thereby forming a teststimulus;

3. causing the tone intensity to decrease to an approximate inaudiblelevel;

4. causing the tone intensity to increase to an approximate barelyaudible level;

5. repeating steps 3 and 4 continuously as the tone frequency graduallyincreases;

6. generating a signal of gradually increasing frequency from 200 Hz to10,000 Hz of a pure tone;

7. pulsating the signal at 2 to 10 pulses per second thereby forming atest stimulus;

8. causing the tone intensity to increase to a level of distinctdiscomfort;

9. causing the tone intensity to decrease to a tolerable level;

10. repeating steps 8 and 9 continuously as the tone graduallyincreases;

1 1. providing the subject with an output from a master prostheticdevice including a general filter network over a general range of acuitydeficiency of the subject as determined by the results of the abovesteps, said general filter network comprising a plurality of individualfilter network;

12. providing the subject with a choice as to the better perception ofcontinuous discourse, between discourse at the output of the masterdevice when the master device is set at different individual filternetworks;

13. determining the best individual filter network to providecorrections of auditory deficiencies in the aurally handicapped subjectin response to the results of step 12; and

14. choosing the prosthetic device having a single filter with the saidcharacteristics of said individual filter network.

7. The method as in claim 1 wherein step 1 includes the step ofrecording the absolute threshold information for the pure tone as afunction of frequency.

8. The method as in claim 1 wherein step 2 includes the step ofrecording the auditory discomfort information for a pure tone intensityas a function of frequency.

9. The method as in claim 1 wherein step 1 includes the step ofrecording absolute threshold information for a pure tone as a functionof frequency and step 2 includes recording auditory discomfortinformation for pure tone as a function of frequency.

10. The method as in claim 1 wherein the following step is added;

6. administering at a conversational loudness level a recordedformalized word test.

11. A method of fitting a prosthetic device having a single filter and aflat gain control by-passing said filter for providing corrections ofauditory deficiencies in an aurally handicapped subject, the methodcomprising the steps of:

1. providing the subject with an output from a master prosthetic device,said master device including a general filter network over a generalrange of acuity deficiency of the subject, said general filter networkincluding a plurality of individual filter network;

2. providing the subject with a choice as to the better perception ofcontinuous discourse, between discourse at the output of the masterdevice set at a first individual filter network and subsequently set atanother individual filter network;

3. determinding the individual filter network to provide corrections ofauditory deficiencies in the aurally handicapped subject in response tostep 2, and

" 4. choosing the prosthetic device having a single filter with the saidcharacteristics of said individual filter network.

12. The method of claim 11 wherein step 3 further includes the step ofdetermining the best combination of individual filter networks toprovide correction of auditory deficiencies in the aurally handicappedsubject.

13. The method of claim 12 wherein step 2 further includes the step ofcontinuously providing the subject with choices between discourse at theoutput of the master device set alternatively to pairs of individualfilter networks until the best individual filter network is determined.

14. The method of claim 13 wherein step 3 further includes the step ofdetermining the best combination of individual filter networks toprovide correction of auditory deficiencies in the aurally handicappedsubject.

1. A method of fitting a prosthetic device having a single filter and aflat gain control by-passing said filter for providing corrections ofauditory deficiencies in an aurally handicapped subject comprising thesteps of:
 1. determining absolute threshold information over apredetermined audio range for a pure tone as a function of frequency; 2.determining information over a predetermined audio range for tonediscomfort level of a pure tone as a function of frequency;
 3. providingthe subject with an output from a master prosthetic device including ageneral filter network over a general range of acuity deficiency of thesubject as determined by the results of step 1 and step 2, said generalfilter network including a plurality of individual filter networks; 4.providing the subject with a choice as to the better perception ofcontinuous discourse between discourse at the output of the masterdevice when the master device is set at different individual filternetworks;
 5. determining the best individual filter network to providecorrections of auditory deficiencies in the aurally handicapped subjectin response to the results of step 4, and
 6. choosing the prostheticdevice having a single filter with the said characteristics of saidindividual filter network.
 2. determining information over apredetermined audio range for tone discomfort level of a pure tone as afunction of frequency;
 2. pulsating the signal at two pulses per secondthereby forming a test stimulus;
 2. The method as in claim 1 whereinstep 1 further comprises the steps of: a. generating a signal ofgradually increasing frequency from 200 Hz to 10,000 Hz of a pure tone;b. pulsating the signal at at a comfortable number of pulses per secondthereby forming a test stimulus; and c. controlling the intensity of thetone of the test stimulus to achieve absolute threshold information. 2.providing the subject with a choice as to the better perception ofcontinuous discourse, between discourse at the output of the masterdevice set at a first individual filter network and subsequently set atanother individual filter network;
 3. causing the tone intensity todecrease to an approximate inaudible level;
 3. The method as in claim 2wherein step (c) further iNcludes the steps of: aa. causing the toneintensity to decrease to an approximate inaudible level; bb. causing thetone intensity to increase to an approximate barely audible level; andcc. repeating steps (aa) and (bb) continuously as the tone frequencygradually increases.
 3. providing the subject with an output from amaster prosthetic device including a general filter network over ageneral range of acuity deficiency of the subject as determined by theresults of step 1 and step 2, said general filter network including aplurality of individual filter networks;
 3. determinding the individualfilter network to provide corrections of auditory deficiencies in theaurally handicapped subject in response to step 2, and
 4. choosing theprosthetic device having a single filter with the said characteristicsof said individual filter network.
 4. providing the subject with achoice as to the better perception of continuous discourse betweendiscourse at the output of the master device when the master device isset at different individual filter networks;
 4. causing the toneintensity to increase to an approximate barely audible level;
 4. Themethod as in claim 1 wherein step 2 further includes the steps of: a.generating a signal of gradually increasing frequency from 200 Hz to10,000 Hz of a pure tone; b. pulsating the signal at 2 to 10 pulses persecond thereby forming a test stimulus; c. controlling the intensity ofthe tone of the test stimulus to achieve auditory discomfortinformation.
 5. The method as in claim 4 wherein step (c) furtherincludes the steps of: aa. causing the tone intensity to increase to alevel of distinct discomfort; bb. causing the tone intensity to decreaseto a tolerable level; cc. repeating steps (aa) and (bb) continuously asthe tone frequency gradually increases.
 5. determining the bestindividual filter network to provide corrections of auditorydeficiencies in the aurally handicapped subject in response to theresults of step 4, and
 5. repeating steps 3 and 4 continuously as thetone frequency gradually increases;
 6. generating a signal of graduallyincreasing frequency from 200 Hz to 10,000 Hz of a pure tone; 6.administering at a conversational loudness level a recorded formalizedword test.
 6. choosing the prosthetic device having a single filter withthe said characteristics of said individual filter network.
 6. A methodof fitting a prosthetic device having a single filter and a flat gaincontrol by-passing said filter for providing corrections of auditorydeficiencies in an aurally handicapped subject comprising the steps of:7. pulsating the signal at 2 to 10 pulses per second thereby forming atest stimulus;
 7. The method as in claim 1 wherein step 1 includes thestep of recording the absolute threshold information for the pure toneas a function of frequency.
 8. The method as in claim 1 wherein step 2includes the step of recording the auditory discomfort information for apure tone intensity as a function of frequency.
 8. causing the toneintensity to increase to a level of distinct discomfort;
 9. causing thetone intensity to decrease to a tolerable level;
 9. The method as inclaim 1 wherein step 1 includes the step of recording absolute thresholdinformation for a pure tone as a function of frequency and step 2includes recording auditory discomfort information for pure tone as afunction of frequency.
 10. The method as in claim 1 wherein thefollowing step is added;
 10. repeating steps 8 and 9 continuously as thetone gradually increases;
 11. providing the subject with an output froma master prosthetic device including a general filter network over ageneral range of acuity deficiency of the subject as determined by theresults of the above steps, said general filter network comprising aplurality of individual filter network;
 11. A method of fitting aprosthetic device having a single filter and a flat gain controlby-passing said filter for providing corrections of auditorydeficiencIes in an aurally handicapped subject, the method comprisingthe steps of:
 12. providing the subject with a choice as to the betterperception of continuous discourse, between discourse at the output ofthe master device when the master device is set at different individualfilter networks;
 12. The method of claim 11 wherein step 3 furtherincludes the step of determining the best combination of individualfilter networks to provide correction of auditory deficiencies in theaurally handicapped subject.
 13. determining the best individual filternetwork to provide corrections of auditory deficiencies in the aurallyhandicapped subject in response to the results of step 12; and
 13. Themethod of claim 12 wherein step 2 further includes the step ofcontinuously providing the subject with choices between discourse at theoutput of the master device set alternatively to pairs of individualfilter networks until the best individual filter network is determined.14. The method of claim 13 wherein step 3 further includes the step ofdetermining the best combination of individual filter networks toprovide correction of auditory deficiencies in the aurally handicappedsubject.
 14. choosing the prosthetic device having a single filter withthe said characteristics of said individual filter network.